The invention relates to a process for the production of highly elastic, open-celled foams containing urethane groups by reacting polyether polyols with modified polyisocyanates in the presence of cross-linking agents and water, optionally in the presence of catalysts, emulsifiers, stabilizers and organic blowing agents characterized in that the reactions are carried out in the presence of cross-linking mixtures corresponding to a specified general formula.
Flexible elastic polyurethane foams have been used very widely in the upholstery industry for the production of padding for seats and back rests. Flexible elastic foams should be comfortable to sit on like foams composed of natural latex or like a combination of conventional padding materials such as spring interiors with natural hair or wadding. The quality of the padding can be determined by the compression factor known as the SAG factor and by the shape of the force-deformation characteristic curves. The SAG factor is the quotient of the hardness numbers at 65% and 25% impression, the total deformation being kept constant for one minute in each case. The SAG factor should be higher than 2.5 in order to obtain a good padding properties, and the force-deformation characteristic curves should not exhibit a plateau, i.e. only slight changes in deformation should occur when the force is changed slightly rather than large changes in deformation. Foams used in the upholstery industry should also be as strong as possible in order to prevent the material from tearing when a mechanical stress is applied, for example when the padding is covered with textiles. Such foams also should be as hard as possible at a given bulk density (kg/m.sup.3). Foams having bulk densities from 15 to 40 kg/m.sup.3 are particularly advantageous economically.
In order to meet these various requirements, attempts have been made to use inert organic or inorganic fillers. It is known to add solid additives to one of the components serving as a foaming agent or directly to the foaming mixture itself, for example by adding fillers directly to the mixing chamber of a foaming machine. Additionally, attempts have been made to carry out polymerization in the polyols used for foaming. For example, dispersions of copolymers of styrene and acrylonitrile in polyethers containing hydroxyl groups are commercially available. However, foams having high degrees of rigidity at a predetermined bulk density cannot be produced or can be produced only with considerable difficulties by methods known in the art.
The objects of the present invention are to overcome these disadvantages and, in addition, to provide foams which can be produced in a commercially simple manner with a wide range of bulk densities and which have high degrees of rigidity at predetermined bulk densities.
These objects can surprisingly be achieved if polyurethane foams are produced from polyether polyols, modified polyisocyanates, water, catalysts, emulsifiers, stabilizers and optionally organic blowing agents, in the presence of the cross-linking agents used in the invention. It is extremely surprising that modified isocyanates already having branch points in the molecule could be combined with the cross-linking agents of the invention to produce highly elastic foams with the desired higher degrees of rigidity since these properties would be expected to be mutually exclusive. Previous experience has shown that a higher degree of cross-linking generally gives rise to products which are more brittle. However, by using the present process, it is possible to produce foams similar in nature to latex foams, but having greater rigidity.